Proportional-integral-differential (PID) control that controls a servo motor such that the position and velocity of the servo motor follow an externally-input position command value and an externally-input velocity command value has been known as a servo motor controlling method. Similarly to the PID control, sliding mode control has been known as the motor controlling method. For example, Unexamined Japanese Patent Publication No. 2011-176906 (published on Sep. 8, 2011) discloses a motor controlling device implementing sliding mode control that controls the position and velocity of a rotor along a sliding curve fixed with a physical variable used in orientation control, thereby stopping the rotor at a target position.
For the PID control, although a user easily recognizes a transmission characteristic, a problem such as overshoot and hunting occurs in the case that a torque to be output is limited. On the other hand, for the sliding mode control, although the control can be implemented such that the overshoot and the hunting do not occur, the user hardly understands the transmission characteristic of a sliding mode controller since the transmission characteristic is nonlinear.